popping from new exhaust and jet kit - Kawasaki KLR 650 Forum
1987 to 2007 Wrenching & Mods For maintaining, repair or modifications of Generation 1 KLR's. 2007 and earlier.

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post #1 of 21 Old 06-17-2010, 09:37 PM Thread Starter
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popping from new exhaust and jet kit

hey all, i recently put a Studabaker exahaust pipe on it, sounds great... installed a 150 main jet and needle from the jet kit. it runs great but if i let off the throttle its starts to pop from the exhaust... ive been turning the air mixture screw a little more and more...im not sure how much more i can go...i believe its at around 3.5 turns out. i also installed a k&n filter...and havent done the air box mod with the L holes on top yet.... do you guys think its still running lean? should i go down to a 140 jet size? or do the air box mod and go from there adjusting the air mixture screw? any help would be appricated!---snuffy
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post #2 of 21 Old 06-18-2010, 12:31 AM
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a little more info about your bike would help greatly.
try putting the stock airfilter back in and see if it changes things.
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post #3 of 21 Old 06-18-2010, 09:36 AM
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Originally Posted by snuffy View Post
hey all, i recently put a Studabaker exahaust pipe on it, sounds great... installed a 150 main jet and needle from the jet kit. it runs great but if i let off the throttle its starts to pop from the exhaust... ive been turning the air mixture screw a little more and more...im not sure how much more i can go...i believe its at around 3.5 turns out. i also installed a k&n filter...and havent done the air box mod with the L holes on top yet.... do you guys think its still running lean? should i go down to a 140 jet size? or do the air box mod and go from there adjusting the air mixture screw? any help would be appricated!---snuffy


Try the search function this has come up quite a bit lately.
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post #4 of 21 Old 06-18-2010, 03:23 PM Thread Starter
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my fault guys, its a 2000 klr 650. the stock air filter was pretty dirty, i dont think i should put that thing back in it. im wondering if i should downsize the jet size to the 140 instead of the 150. and i was thinking maybe doing the "L" mod to the air filter would help it out some. but what the hell do i know?!
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post #5 of 21 Old 06-18-2010, 04:11 PM
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Originally Posted by snuffy View Post
my fault guys, its a 2000 klr 650. the stock air filter was pretty dirty, i dont think i should put that thing back in it. im wondering if i should downsize the jet size to the 140 instead of the 150. and i was thinking maybe doing the "L" mod to the air filter would help it out some. but what the hell do i know?!
Well, snuffy, popping on decel is an indication a lean condition, as you know.

Doing the L-Mod will (theoretically) allow more air into the engine, leaning the mixture, so that's probably not what you want to do at this point.

As to the 150 jet, I just don't know what the Studebaker stuff is. See, a 150 jet ain't a 150 jet all the time. The thing about jets is that everybody has their own standard. Kinda defeats the purpose of standards....

A 150 Keihin jet would be awfully rich - there's no configuration on the KLR that would warrant it. The head just won't flow enough, no matter what you do to the exhaust and intake, to use that much jet. Well, maybe a 685 kit, ported head, big valves and a really free flowing pipe...nah, doubt even then.

You've got several things going that are somewhat contradictory. You put on an exhaust, which ought to flow better, leaning the mixture. But you've installed some sort of 150 jet, which may be bigger than stock (probably is) but you've also installed a needle that we don't know the profile of. It's hard to judge what the net effect is.

The K&N is reputed to be more restrictive than the stock, so that would richen things up a bit (I bet you could clean that old stock filter!).

You've also turned the mixture screw out, which should richen the idle circuit, but you've still got popping.

My advice would be to put the stock jet and needle back in, but with two stainless #4 washers under the head.

Turn the mixture screw in until it is gently seated, then back it out 2 turns.

See how things are working then, and we can go from there.

Now, on that jet and needle - do you have anyway to measure (pin gauges) the size of the 150 jet? Or did the jet kit come with a table that tells you what size it is? Do you have a way to chart out the taper of the needle that came with the kit? I can provide you with a table of Keihin jet sizes and the taper of the stock needle and of a KLX needle for reference. That may come in handy for later tuning once you get that popping under control.

A word on the idle circuit. I have made what I consider to be pretty extreme mods to my intake and exhaust. I found that the stock idle jet to be too small for my mods and had to go up a size. Resist the urge to solve your problem by going to a larger idle jet. I can tell you that your mods have to be pretty extreme to need that. If you do such a thing (not saying you're contemplating it!) you might solve the problem, but you've really just masked what the real problem is.

Do you have a way to check the air/fuel ratio? If you have good records of gas mileage, you can make changes and check the gas mileage to see if it's gotten better or worse - slow, but effective. Are you familiar with reading plugs? Maybe have a wideband O2 meter? To make this all work right you're going to need to be fairly certain that your mixture is correct.

Tom

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Last edited by Tom Schmitz; 06-18-2010 at 04:19 PM.
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post #6 of 21 Old 06-18-2010, 05:37 PM
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I have an 09 with the IDS2 exhaust on it. The previous owner said he had it adjusted for the exhaust, But I still get the same as you, popping on decel and on let of of gas sometimes. I'll fool around with it and see what happens I guess.
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post #7 of 21 Old 06-19-2010, 03:12 PM Thread Starter
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thanks tom for that advice! well before i got your reply back, i went and did the L air box mod....still with the 150 main jet in the carb i took it for a test ride....was fine at first it seemed then i started hearing a few pops. am i not suppose to hear one pop from the exhaust even if its reved up at 7 grand for some reason?
the jet kit is a "dyno jet" kit. i have no idea if its a keihin jet or not. i followed the instructions in the jet kit paperwork. the new needle i know has grooves on the top where i had to put an E clip on the forth groove and then two washers above that.
i just compared the stock jet to the 140 jet and the stock ones looks bigger. i suppose i can go back to the stock jet and needle with the two washers on it if you'd think that would help. its worth a shot
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post #8 of 21 Old 06-19-2010, 04:35 PM
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Make sure you don't have an exhaust leak because that will cause popping on decel and it won't change with jetting.
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post #9 of 21 Old 06-19-2010, 05:01 PM
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Keep in mind, we can't hear, see or smell what is going on at your end. Considering the main jet you have in there, and the 3.5 turn out setting on the idle mix screw, running lean may not be the issue. You put on a new muffler. What kind of connection did you get behind the rear brake reservoir, where the exhaust pipe and muffler connect? If that connection is not air tight, it could produce "popping on deceleration".

Reading your spark plug should tell you something about a lean setting. Pull it, and see if it is displaying a noticeable white color on the end. Not the porcelain end. The end in that was in the head. Don't mean to be rude, but I have learned to assume nothing.

Now for my own biased, unasked for opinion: The "22 cent mod" would have achieved everything performance wise that you were hoping to gain from all these add ons. If you were looking for a new hobby of messing around with carburetors for as long as you ride this bike, you are on the right path.

As it is right now, nobody really knows if your bike is drawing more or less air than before you began. Nobody really knows how much exhaust back pressure relief comes with the Studebaker muffler. I don't see any modifications that warrant a DJ 150 jet. My suggestions run along the lines of what Tom suggested: put the stock 148 jet back in there. Set your air mix screw at about 2.75 turns out. I would try leaving the DJ needle in, and set the clip on the third groove from the top. You did drill the slide, right? 7/64 is as big as you need to go....You will experience a noticeable immediate response when you hit the throttle. Noticeable. Not "roll you off the back of the bike" awareness, but a response worth the effort. You can mess with this forever, and still come to the same conclusion a lot of us have. There ain't no replacement for displacement.
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post #10 of 21 Old 06-19-2010, 05:26 PM Thread Starter
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well vatrader.... i pulled the plug and noticed a whitish color on the end of the plug. and yes im about to throw this bike over a cliff im so frustrated right now. the exhaust seems fine, checked all the connections and seem tight, retightened the bolts to make sure. didnt expect to be screwing with this carb for so dam long! alright ill put the stock jet back in, leaving the dyno jet needle and set it on the third groove instead of the forth. and yes i did drill the hole in the slide with the provided drill bit they gave me in the slide. ill keep ya posted
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